Waterproof Vapor-Permeable Multilayer Article

ABSTRACT

A waterproof vapor-permeable multilayer article, comprising at least one first layer made of a material that is vapor-permeable and microporous and is at least partially hygroscopic or can assume hygroscopic characteristics over time, and at least one second layer that is waterproof and vapor-permeable.

TECHNICAL FIELD

The present invention relates to a waterproof vapor-permeable multilayerarticle.

BACKGROUND ART

Waterproof vapor-permeable multilayer articles, constituted in practiceby a membrane based on polytetrafluoroethylene, are currently knownparticularly in the field of shoes and clothing.

Such membrane is coupled to the fabrics that compose the item ofclothing in order to allow correct permeation of the water vapor thatforms due to perspiration released by the body within the environmentdelimited by the item of clothing.

At the same time, the item of clothing must allow correct waterproofing,with the same goal of keeping the body dry.

The same occurs for shoes: membranes of this type are associated withthe upper and with the sole of the shoe; in this regard, it should benoted that most of the perspiration of the foot originates at theinterface between the sole of the foot and the sole of the shoe.

Currently known membranes, though having been used now for several yearsand being unanimously acknowledged as being capable of ensuring correctwaterproofing and optimum permeability to water vapor and air,nonetheless have aspects that can be improved.

These membranes are scarcely resistant, and in fact they can teareasily: to give them strength, they are therefore coupled, generally bylamination, to a supporting mesh made of plastic material, whichinevitably reduces their permeability to water vapor or air.

In any case, coupling to the mesh is not sufficient to achieveacceptable strength characteristics.

In view of the limited consistency of these membranes, it is evidentthat such membranes are not capable of being self-supporting.

For this reason, for example in soles, the membrane (which is integratedwith the mesh) must be coupled to supports that are capable ofsupporting it adequately.

Moreover, it should be noted that when, for any particular reason,perspiration condenses inside the environment to be kept dry, which isdelimited by said membranes, such perspiration can no longer beexpelled, causing an unpleasant “wet” effect.

DISCLOSURE OF THE INVENTION

The aim of the present invention is to provide a waterproofvapor-permeable multilayer article that solves the drawbacks noted inknown types.

Within this aim, an object of the present invention is to provide awaterproof vapor-permeable multilayer article that is structurallystrong.

Another object of the present invention is to provide a waterproofvapor-permeable multilayer article that is particularly permeable tovapor or air.

Another object of the present invention is to provide a waterproofvapor-permeable multilayer article that is capable of beingself-supporting.

Another object of the present invention is to provide a waterproofvapor-permeable multilayer article that can be manufactured with knownsystems and technologies.

This aim and these and other objects of the present invention that willbecome better apparent hereinafter are achieved by a waterproofvapor-permeable multilayer article, characterized in that it comprisesat least one first layer made of a material that is vapor-permeable andmicroporous and is at least partially hygroscopic or can assumehygroscopic properties over time, and at least one second layer that iswaterproof and vapor-permeable.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the invention will becomebetter apparent from the description of two preferred but not exclusiveembodiments thereof, illustrated hereinafter by way of non-limitingexample in the accompanying drawing, wherein:

FIG. 1 is a sectional view of a first embodiment of a multilayer articleaccording to the invention;

FIG. 2 is a sectional view of a variation of the multilayer article ofFIG. 1;

FIG. 3 is a sectional view of a second embodiment of a multilayerarticle according to the invention;

FIG. 4 is a sectional view of a variation of the multilayer article ofFIG. 3.

WAYS OF CARRYING OUT THE INVENTION

With reference to the first embodiment, shown in FIG. 1, a waterproofvapor-permeable multilayer article according to the invention isgenerally designated by the reference numeral 10.

The multilayer article 10 comprises a first layer 11, made of a materialthat is vapor-permeable, microporous and hygroscopic, and a second layer12, which is waterproof and vapor-permeable.

The first layer 11 is constituted for example by a hygroscopic materialbased on polyolefin and filler particles.

The filler particles are designed to create the micropores that allowpermeability to vapor or air.

The polyolefin that is used in the example being described has a veryhigh molecular weight; for this reason, such polyolefin is preferably aUHMW (ultra high molecular weight) polyethylene.

The characteristics of a UHMW polyolefin are referred to a polyolefinwith an average molecular weight of at least 500.000 g/mole.

Preferably, the average molecular weight is comprised between 4×10⁶g/mole and 7×10⁶ g/mole.

The preferred filler is a finely milled silica (silicon dioxide, SiO₂).

Silica has an important hygroscopic capacity, to the full advantage ofthe hygroscopic properties of the first layer 11.

The optimum average diameter of the filler particles of silicon dioxideSiO₂ are comprised between 0.01 and 20 μm, while the average surfacearea of said fillers is comprised between 30 m²/g and 950 m²/g.

Preferably, the average surface area of the filler particles is at least100 m²/g.

The first layer 11 being described has a pore size of less than 1 μm indiameter.

Preferably, over 50% of the pores have a diameter of less than 0.5 μm.

Porosity understood as:Porosity=[1−(apparent membrane density/resin density)]×100

is preferably at least 50%.

The first layer 11 is for example treated with antibacterial and/orfungicidal agents.

The preferred final form is a sheet of preset thickness, substantiallycomprised between 200 μm and 1.5 cm; in particular, between 200 and 600μm.

A microporous membrane known by the trade-name DARAMIC® and manufacturedby DARAMIC Inc. (Norderstedt, Germany) has the characteristics describedabove for the first layer 11 and therefore can be used to form amultilayer article according to the invention.

Such microporous membrane is per se known and is currently used as apartition in accumulators and batteries and is provided in sheet form.

The characteristics of the membrane are disclosed in U.S. Pat. No.3,351,495 (in the name of W R GRACE & Co.) and U.S. Pat. No. 6,139,759(in the name of Daramic Inc.).

The version with a thickness of 600 μm of said DARAMIC® membrane has anultimate tensile strength of substantially 5.8 MPa and a maximumbreaking elongation of 505% (according to ISO 37): accordingly, it hasexcellent strength characteristics.

In this first described embodiment, the second layer 12, which iswaterproof and vapor-permeable, is constituted by a hydrophobicmicroporous material based on polypropylene (where the term“polypropylene” is used to designate any polymer, homopolymer orcopolymer originating from propylene monomers).

Preferably, the polypropylene of the second layer 12 is an isotactichomopolymer with low affinity for the absorption of proteins and fats.

A hydrophobic membrane known by the trade-name CELGARD® of the companyCELGARD Inc. has the characteristics described above for the secondlayer 12 and therefore can be used to form a multilayer articleaccording to the invention.

The coupling between the first layer 11 and the second layer 12 occursdepending on the type of “appearance” that said layers have at the timeof coupling.

For example, if both the first layer 11 and the second layer 12 are insheet form, they can be coupled by applying spots of adhesive, so as toavoid creating a compact layer, or by using known high-frequency orultrasound technologies, avoiding the subtraction of breathable surface.

An alternative is for example to spread or roll one layer onto theother, which is considered as a backing.

In this case, the spread layer must strongly adhere to the underlyingbacking so as to resist separation.

Moreover, such layer must have the characteristic of being easy to formor place on the underlying layer by means of large-scale spreading androlling techniques.

The polymeric polyethylene layer of the DARAMIC® membrane can besuitable for spreading, since its molecular weight is high enough toprevent its penetration into the pores of the microporous support, orcan be dispersed in aggregates that are larger than the pores of theCELGARD® polypropylene membrane.

For example, one method for producing a multilayer article according tothe invention is as follows:

-   -   a solution or dispersion of the basic polymeric mix for the        first layer 11 in a volatile organic liquid with low surface        tension is prepared in order to produce a spreading solution        that has a certain viscosity;    -   the solution is applied by spreading to the surface of the sheet        of the second layer 12 that acts as a backing, in order to form        a coating layer on its surface;    -   the volatile components of the spread are made to evaporate in        order to promote the cross-linking reaction of the spread        surface;    -   the coating is dried in order to remove the residual humidity to        produce the laminated article.

It is evident that one or more additional layers of polymer can beapplied likewise and dried in order to reach the intended thicknesses.

The solution of the polymer can be applied to the backing made ofhydrophobic microporous membrane by means of standard spreadingtechniques that are known in the background art, for example rollerspreading or spray spreading.

One variation to the basic configuration of the multilayer article 10composed of two individual layers is shown in FIG. 2.

In this variation, the multilayer article according to the invention,generally designated by the reference numeral 100, is composed of afirst layer 111 made of vapor-permeable microporous hygroscopicmaterial, which is delimited in a sandwich-like fashion by two secondlayers 112 that are waterproof and vapor-permeable.

It is evident that the first layer 111 and the second layers 112respectively have the same characteristics described earlier for thefirst layer 11 and the second layer 12.

Moreover, it is evident that other variations may have superimpositionsof one or more of said first and second layers, combined according tothe requirements.

A second layer 12 (or 112) can also be provided by spreading afluoropolymer on a first microporous layer 11 (or 111) or optionally apolysiloxane.

For example, such fluoropolymer is the one commercially known by thetrade name Zonyl® and manufactured by DuPont.

The second layer 12 (or 112) can also be provided by immersing the firstlayer 11 (or 111) in a bath of a fluoropolymer (for example Zonyl®) orof a polysiloxane.

A second embodiment (see FIG. 3) of a multilayer article according tothe invention, generally designated by the reference numeral 200, has afirst layer 211 such as the one described in the above examples and has,as its second layer, designated here by the reference numeral 212, afilm obtained by means of a plasma deposition treatment.

The idea of the film by plasma deposition arises from the surprisingexperimental discovery that a vapor of a siloxane organic compound canbe used to produce an ultrathin layer on a microporous backing materialby “cold plasma” polymerization in high vacuum at ambient temperature,providing waterproofing characteristics without altering the generalcharacteristics and particularly the permeability characteristics of thebacking material.

A waterproof and breathable hydrophobic layer can in fact be provided byplasma polymerization for example of a monomer based on siloxane, bydepositing a layer of polymer (polysiloxane) on a microporous backingmaterial (for example made of polyethylene or polystyrene).

This deposition can also be performed for example by using oil-repellentand water-repellent fluoropolymers such as those produced by DuPont andregistered with the trade name Zonyl®.

Plasma is divided into hot and cold depending on the temperaturesreached; it is also divided into ambient-pressure plasma and vacuumplasma.

In a cold plasma process to obtain a film according to the presentinvention, a gaseous or vaporized precursor compound is introduced in areaction chamber at a very low pressure (in vacuum conditions).

A plasma condition is generated by energizing the precursor inside thereaction chamber by generating an electrical field.

The result is an ultrathin layer of the polymer, which adheres to, andis deposited on, the entire surface of any substrate material introducedin the reaction chamber.

The plasma polymerization process is started and performed by means ofan electrical field so as to achieve breakdown of the precursor of thedeposition layer within the reaction chamber.

Once breakdown has occurred, ions and reactive species are formed whichbegin and produce the atomic and molecular reactions that ultimatelyform thin films.

Layers created by plasma polymerization can use various configurationsof electrical fields and different reaction parameters.

The thickness of the layer is controlled by selecting the initialpolymerizable material and the reaction conditions, such as thedeposition time of the monomer, the treatment time, the electricalfrequency at which the reaction is performed, and the power used.

In the present invention, plasma polymerization is performed in vacuum.

The typical pressure range is between 10⁻¹ and 10⁻⁵ mbar.

The precursor is made to react in its pure state by using anon-polymerizable inert gas, such as for example argon; such inert gasis used both as an inert dilution agent and as a carrier gas thatassists the polymerization of the precursor.

Other gases that can be used are any of oxygen, helium, nitrogen, neon,xenon and ammonia.

The precursor must have a vapor pressure that is sufficient to be ableto vaporize in a moderate vacuum.

The plasma deposition process begins by loading the backing material tobe coated (in this case, the first layer 212) into the reaction chamberand then bringing the chamber to the intended vacuum pressure.

Once the vacuum pressure has been reached, the plasma polymerizationreaction or a pretreatment reaction can begin.

The plasma polymerization reaction occurs by producing the dischargethat generates the plasma and by injecting the vaporized precursormonomer into the reaction chamber.

A pretreatment reaction is required when the surface of the first layeris to be cleaned by subjecting it to an inert gas such as argon ornitrogen in order to clean the surface or promote the adhesion of thepolymer film.

During the plasma generating discharge, the collision of the monomerwith the ions and electrons of the plasma allows polymerization of themonomer.

The resulting polymer is deposited on the exposed surfaces inside thechamber.

The properties of the film are not just a function of the structure ofthe monomer but also a function of the discharge frequency, of the powerused, of the monomer flow-rate and, of the pressure.

Porosity, surface morphology and permeability can vary according to thereaction conditions.

The deposition process ends when the intended thickness of depositedmaterial is reached.

Owing to the fact that the first layer 212 is made of insulatingmaterial (polyethylene, for example, is one of the most insulatingmaterials known), in order to maintain the plasma conditions it isnecessary to apply to the process a radiofrequency generator in order tomake the electrical field in the treatment oscillate with a frequencysubstantially on the order of 13.56 MHz, with an applied electric fieldpower substantially equal to 50-700 watts and a vacuum level comprisedbetween 10⁻¹ and 10⁻⁵ mbar.

As regards the duration of the treatment, it has been observed that fora precursor such as a siloxane monomer, the optimum time issubstantially comprised between 160 and 600 seconds; in particular, anoptimum duration of substantially 420 seconds has been identified.

One variation to the basic configuration of the multilayer article 200composed of two individual layers is shown in FIG. 4.

In this variation, the multilayer article according to the invention,generally designated by the reference numeral 300, is composed of afirst layer 311 made of vapor-permeable and hygroscopic microporousmaterial, which is delimited in a sandwich-like fashion by two secondslayers 312, which are waterproof and vapor-permeable.

It is evident that the first layer 311 and the second layers 312respectively have the same characteristics described earlier for thefirst layer 211 and the second layer 212.

Moreover, it is evident that other variations may have superimpositionsof one or more of the first and second layers, combined according to therequirements.

In practice it has been observed that the invention thus describedsolves the problems noted in known types of waterproof andvapor-permeable multilayer article.

A multilayer article has in fact been provided which associates a firstmicroporous and hygroscopic layer with a second hydrophobic layer, saidlayers preventing the inflow of any liquid phase while allowing thetransfer of water vapor and other volatile components.

The silicon-based filler provided inside the first layer in order togenerate the microporous structure is a highly hygroscopic material thathas a great tendency to absorb water: accordingly, the first layer isnot appropriate to be used individually as a waterproof layer, but isvery useful for conveying perspiration and moisture away from the body(the torso or legs in the case of clothing, the feet in the case ofshoes).

Moreover, since the first hygroscopic layer and the second hydrophobiclayer are both structurally stronger than the membranes currently usedand are thicker, they can be used in combination without backings thatreduce their permeability to vapor or air.

In this regard, since the multilayer article (10, 100, 200, 300 etcetera) has structural characteristics, it can be used as a supportingstructure of a shoe; for example, in combination with a tread that hasupward openings, the multilayer article can be used as a supportingelement of a breathable and waterproof sole.

Such layers can be coupled, depending on the requirements, by applyingspots of adhesive so as to avoid creating a compact layer or by usingknown high-frequency or ultrasound technologies, avoiding thesubtraction of breathable surface, or by spreading or rolling of onelayer onto the other.

In this regard, since the first layer is the one that reaches greaterthicknesses without compromising vapor and air permeability, by using itas a backing for the plasma deposition of a waterproof breathable film,it is possible to achieve the same above mentioned aim and objects bypairing the two layers by spreading, rolling or adhesive bonding.

It should be noted that the use of plasma deposition solves the problemsof conformity and adhesion of the first layer on the second layer, sincethe plasma-deposited polymer adheres to the backing layer for a longertime than, for example, a conventional spreading.

Moreover, since the waterproof film is deposited in partial vacuumconditions, and since the backing material can be cleaned in thereaction chamber beforehand with argon with a high degree of purity, anyimpurities that could generate fractures, discontinuities, distortionsof the deposited waterproof film are completely avoided.

The invention thus conceived is susceptible of numerous modificationsand variations, all of which are within the scope of the appendedclaims; all the details may further be replaced with other technicallyequivalent elements.

In practice, the materials used, so long as they are compatible with thespecific use, as well as the dimensions, may be any according torequirements and to the state of the art.

The disclosures in Italian Patent Application No. PD2003A000314 fromwhich this application claims priority are incorporated herein byreference.

1-38. (canceled)
 39. A waterproof vapor-permeable multilayer article, comprising: at least one first layer made of a material that is vapor-permeable and microporous, said first layer material being further selected from a group comprising materials that are at least partially hygroscopic and material that can assume hygroscopic characteristics over time; and at least one second layer that is waterproof and vapor-permeable.
 40. The multilayer article according to claim 39, wherein said at least one first layer comprises a base of polyolefin and a filler made of filler particles.
 41. The multilayer article according to claim 40, wherein the molecular weight of said polyolefin is at least 500,000 g/mole.
 42. The multilayer article according to claim 41, wherein the molecular weight of said polyolefin is between 4×10⁶ g/mole and 7×10⁶ g/mole.
 43. The multilayer article according to claim 40, wherein said polyolefin is constituted by a material selected from a group consisting of isotactic polypropylene and polyethylene.
 44. The multilayer article according to claim 40, wherein said filler is silicon dioxide SiO₂.
 45. The multilayer article according to claim 44, wherein an average diameter of the filler particles of silicon dioxide SiO₂ is substantially between 0.01 pm and 20 μm, while an average surface area of said fillers is substantially between 30 m²/g and 950 m²/g.
 46. The multilayer article according to claim 44, wherein an average surface area of said filler particles is at least 100 m²/g.
 47. The multilayer article according to claim 39, wherein said at least one first layer made of microporous material has a pore size of less than 1 μm in diameter.
 48. The multilayer article according to claim 47, wherein more than 50% of the pores of said at least one first layer made of microporous material have a diameter of less than 0.5 μm.
 49. The multilayer article according to claim 48, wherein the porosity of said at least one first layer made of microporous material is at least 50%.
 50. The multilayer article according to claim 39, wherein said at least one first layer made of microporous material has a thickness comprised between 200 μm and 1.5 cm.
 51. The multilayer article according to claim 50, wherein said at least one first layer made of microporous material has a thickness between 200 μm and 600 μm.
 52. The multilayer article according to claim 39, wherein said at least one first layer is constituted by a microporous membrane that is available on the market.
 53. The multilayer article according to claim 39, wherein said at least one second waterproof vapor-permeable layer is constituted by a polypropylene-based microporous hydrophobic material.
 54. The multilayer article according to claim 53, wherein the polypropylene of said microporous hydrophobic material is an isotactic homopolymer.
 55. The multilayer article according to claim 53, wherein said at least one second layer is constituted by a hydrophobic membrane that is available on the market.
 56. The multilayer article according to claim 39, wherein said at least one second layer is composed of a polymer based on fluoropolymer or polysiloxane, said at least one second layer adhering to said first layer by spreading or immersing said first layer in a bath of said polymer.
 57. The multilayer article according to claim 56, wherein said fluoropolymer is a material that is available on the market.
 58. A method for manufacturing a multilayer article as set forth in claim 39, consisting of: preparing a solution or dispersion of a basic polymeric mix for a first layer in a volatile organic liquid with low surface tension, in order to produce a spreading solution that has a certain viscosity; applying said solution by spreading to a surface of a second layer, which acts as a backing, in order to form a coating layer on the surface thereof; evaporating volatile components of the spread in order to promote cross-linking reaction of the spread surface; and drying the coating in order to remove the residual humidity.
 59. A method for producing a multilayer article as set forth in claim 39, which consists of coupling a first layer and a second layer by lamination of one of said layers onto the other.
 60. A method for producing a multilayer article as set forth in claim 39, which consists of coupling a first layer in sheet form to a second layer, also in sheet form, by any of an adhesive spot application, by ultrasound and by high-frequency welding.
 61. The multilayer article as set forth in claim 39, comprising the step of providing at least one second layer of material that is constituted by a film obtained by way of a plasma deposition treatment.
 62. The multilayer article of claim 61, wherein the step for plasma deposition treatment is carried out by working in high-vacuum cold plasma conditions.
 63. The multilayer article of claim 62, wherein said step for plasma deposition treatment is carried out by using a radiofrequency generator so that an electrical field in the treatment oscillates with a frequency substantially between 13 MHz and 14 MHz.
 64. The multilayer article according to claim 63, wherein said step for plasma deposition treatment is carried out by using a radiofrequency generator so that an electrical field in the treatment oscillates with a frequency on the order of 13.56 MHz.
 65. The multilayer article of claim 64, wherein the step for plasma deposition treatment is carried out by using a power of the electrical field applied in the treatment that is substantially between 50 watts and 700 watts.
 66. The multilayer article of claim 65, wherein the duration of said plasma deposition treatment for a siloxane-based monomer is between 160 and 600 seconds.
 67. The multilayer article according to claim 66, wherein the duration of said plasma deposition treatment for a siloxane-based monomer is substantially equal to 420 seconds.
 68. The multilayer article according to claim 67, wherein the level of vacuum in said plasma deposition treatment is substantially between 10⁻¹ mbar and 10⁻⁵ mbar.
 69. The multilayer article according to claim 61, wherein the step for plasma deposition treatment is carried out by working in high-vacuum cold plasma conditions and by using a radiofrequency generator so that an electrical field in the treatment oscillates with a frequency on the order of 13.75 MHz, with an applied electrical field power of 300-500 watts, and a vacuum level comprised between 10⁻¹ and 10⁻⁵ mbar.
 70. The multilayer article of claim 69, wherein the plasma deposition precursor material is a siloxane-based monomer.
 71. The multilayer article according to claim 69, wherein the plasma deposition precursor material is an oil-repellent and water-repellent fluoropolymer.
 72. The multilayer article of claim 69, wherein the material of said at least one second layer is a polysiloxane.
 73. The multilayer article according to one of claim 69, wherein the material of said at least one second layer is an oil-repellent and water-repellent fluoropolymer.
 74. The multilayer article of claim 73, wherein said fluoropolymer is a material available on the market.
 75. A method for producing a multilayer article according to claim 72, comprising the steps of: loading the first layer to be coated into a reaction chamber; bringing the reaction chamber to a preset vacuum pressure; starting plasma generating electrical discharge; injecting vaporized precursor monomer into said reaction chamber; and waiting for a preset deposition time.
 76. A production method according to claim 75, comprising a pretreatment step that consists of the surface cleaning of said first layer by subjecting it to an inert gas that is injected into said reaction chamber. 